Exchanges in the Baltimore-Washington region



Today, Baltimore and Washington are really two different metropolitan areas, and so I'm not really happy about grouping them together in one section of this website. But there was a time when the two cities were within local calling distance of each other, and so there were constraints on exchange names that require treating the entire Baltimore-Washington region as a unit.

The site will treat the region as a combination of the following areas:

  1. The city of Baltimore
  2. The suburban areas around Baltimore
  3. The suburban areas in Maryland around Washington, D. C.
  4. The District of Columbia (Washington, D. C.)
  5. The suburban areas in Virginia around Washington, D. C.

Since both the Baltimore and washington suburbs (as well as the city of Baltimore) were in the same 301 area code (Note that this has changed, but the new 410 area code for Baltimore and eastern Maryland was many years in the future in the period dealt with on this site) all three had to have distinct exchanges even after the end of local dialing between the Baltimore and Washington areas, so that callers outside the 301 area could dial 301 and the appropriate number to be connected with their intended person. But since (until the 1990s) subscribers in Washington, D. C. and its suburban areas could dial to points in the entire area consisting of the District of Columbia and its Maryland and Virginia suburbs without needing to dial an area code, all three of these portions of the region also had to have distinct exchanges.

While it would be possible to consider Baltimore and its suburbs as a single area for the purposes of this site, I do not think it desirable. For me anyway, it is better to separate city and suburban exchanges into different tables, so I will do so. But even so, there were the following constraints:

  1. Baltimore city and suburban exchanges had to be different from exchanges in the Washington suburbs in Maryland, because of the 301 area code (and in fact were constrained by other exchanges in Maryland outside of the region), but could (after the end of Baltimore-Washington local dialing) overlap with D. C. and Virginia exchanges,
  2. Washington suburban exchanges within Maryland could not overlap with Baltimore city and suburban exchanges, because of the 301 area code, nor could they overlap with the the District of Columbia and Virginia suburban exchanges, because of the Washington Metropolitan Dialing Area, and so were the most rigidly constrained of all the exchanges in the region,
  3. District of Columbia exchanges could overlap (after the end of Baltimore-Washington local dialing) with Baltimore city and suburban exchanges, but had to be distinct from exchanges in the Washington suburbs within both Maryland and Virginia,
  4. Washington suburban exchanges within Virginia, like the D. C. exchanges, could overlap (after the end of Baltimore-Washington local dialing) with Baltimore city and suburban exchanges, but besides being distinct from exchanges both in the District of Columbia and the Washington suburbs in Maryland because of the Washington Metropolitan Dialing Area, needed to be distinct from exchanges in the entire 703 area code (originally the entire state of Virginia, but, after a split in the 1970s that created the 804 area code, only the northern and eastern parts of the state). Since the creation of the 804 area code was after most of the period covered here, one can really say that they needed to be distinct from exchanges in the entire state of Virginia.

Separate sets of tables have been prepared for each area. Clicking the name of the area in the listing of the five areas above will get you to the appropriate set of tables.


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Last modified February 6, 2009.

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